A method of obtaining a platinum-rhodium or palladium-rhodium catalyst on a ceramic carrier

 

(57) Abstract:

A method of obtaining a platinum-rhodium or palladium-rhodium catalyst on a ceramic carrier by successive impregnation of the carrier with aqueous solutions of platinum(palladium)-containing compound and the rhodium-containing compound, followed by drying and calcination of the catalyst is characterized by the fact that in order to obtain a homogeneous distribution of PT(PD) + Rh with a ratio of 1 : 1 carrier impregnated with a solution of dichlorethylene platinum (II) PT(NH3)4Cl2or palladium (II) Pd(NH3)4Cl2, dried, followed by treatment with a solution of ammonium salt of rhodium hexachloride (NH4)[RHCl6] with the formation on the surface of the carrier partially soluble binuclear complex [M(NH3)4][RhL6], where M = PT (II) or Pd(II), a L = CL-and H2O. Technical result is an increase in the activity of the catalysts at low temperatures (150-160C). table 4.

The invention relates to catalytic chemistry, in particular to methods of producing catalysts for neutralization of exhaust gases of internal combustion engines.

One of the main requirements for modern TWC (trifunctional catalysts) catalysis is about when the operating mode, but at the time of engine start. This problem can be solved by additional activity of Pt/Pd/Rh catalyst, deposited on a well-developed ceramic substrate.

Known methods for producing catalysts for the conversion of fuel combustion products, based on the impregnation of the ceramic substrate, mainly - Al2O3, solution managernew compounds of platinum metals with subsequent recovery of the metal.

The disadvantage of these methods is the lack of homogeneity in the distribution of two or more platinum group metals in the surface layer, which reduces the catalyst activity [R. M. Heck, R. J. Farrauto. Catalytic air pollution control New York. Van Noctrand Reinhold. 1995. p. 42].

The closest in technical essence of the present invention is a method of obtaining a Pt/Rh catalyst by successive impregnation of the ceramic substrate (Al2O3) aqueous solutions of first Pt(NO2)2(NH3)2then rhodium nitrate, followed by calcination at a temperature of 600oC [US 5063192, 05.11.1991]. This catalyst provides a 95 - 100% conversion of NOx, CO and HC at a temperature above 250oC.

The disadvantage of this method is the unevenness of the soap is activity in the conversion of hydrocarbons, an oxide of nitrogen and carbon monoxide in the temperature range of 150 - 160oC, i.e. at the start of the operation of the internal combustion engine that is required under generally accepted in Europe (including Russia) Directive EURO-2. In addition, a known catalyst of low activity (conversion ~ 50%) at a temperature of 200 - 250oC with respect to all of the major toxic components of exhaust gas.

The aim of the present invention is to increase the catalyst activity at low temperatures (150 - 160oC).

According to the invention this goal is achieved by the fact that the catalyst is obtained by impregnation of the carrier (mostly-Al2O3first solution dichlorethylene platinum (II) or palladium (II) [Pt(NH3)4Cl2or [Pd(NH3)4] Cl2followed by drying and treatment with a solution of ammonium salt of rhodium hexachloride to obtain on the surface of the carrier partially soluble binuclear complex with the formula [M(NH3)4][RhL6], where M is Pt (II) or Pd (II) and L = Cl-H2O with further drying and calcining the catalyst at a temperature of 550 - 620oC.

Distinctive features of the method are:

the impregnated carrier rest is produced media;

treatment with a solution of ammonium salt of rhodium hexachloride (NH4)3[RhCl6].

While in the pores of the carrier is formed partially soluble binuclear complex [M(NH3)4][RhL6], where M is Pt (II) or Pd (II) and L = Cl-H2O. the composition of the compound confirmed by chemical and x-ray phase analysis, IR spectroscopy. By thermal decomposition of this complex is obtained catalyst with uniform distribution of platinum group elements in the layer thickness of the substrate to 4000 . From the above equation formed binuclear complex shows that the ratio of it M : Rh = 1 : 1. Therefore, after annealing in the surface of the carrier evenly distributed two metal (M and Rh) in a 1 : 1 ratio. However, if the receiving process on the surface of the carrier binuclear complex pre-applied platinum, you can get a ratio of 5 : 1 or 5 : 2 (Pt : Rh or Pd : Rh, respectively), typical catalysts used in the automotive industry.

The method is as follows: a ceramic substrate, for example-Al2O3soaked in an aqueous solution of [Pt(NH3)4]Cl2or [Pd(NH3)4]Cl2,

relying on Blagoev at 100 120oC, is placed in a vessel with an aqueous solution of (NH4)3[RhCl6], dried and calcined for one hour at a temperature of 550 - 620oC.

The choice of concentration of the compound of rhodium is determined by what must be the ratio of Pt (Pd) : Rh = 1 : 1. When the impregnation of the sample in an aqueous solution of (NH4)3[RhCl6] in the pores of the ceramic substrate is formed manorastroman compound of composition [M(NH3)4][RhL6] that prevents you from changing the concentration of Pt (Pd) in a ceramic matrix and forms the ratio of Pt (Pd) : Rh in the surface layer in accordance with the structure of the formed complex.

Example 1.

100 grams of granulated-Al2O3brand EE-2 impregnated with 150 ml of an aqueous solution containing [Pt(NH3)4]Cl2of 1.88 mg/ml Then the granules are dried in air for 1.5 - 2 hours at a temperature of 100 - 150oC, then placed in a 150 ml aqueous solution containing (NH4)3[RhCl6] 2,14 mg/ml After the granules are dried in air and calcined for one hour at a temperature of 550 - 620oC. the resulting catalyst contains 0.05 wt.% Pt + Rh ratio ~ 1 : 1.

Example 2.

The catalyst was prepared analogously to example 1.

the military, the catalyst contains 0.1 wt.% Pt + Rh ratio ~ 1 : 1.

Example 3.

The catalyst was prepared analogously to example 1.

However, the concentration of [Pt(NH3)4] Cl2was 13,73 mg/ml, and (NH4)3[RhCl6] - 17,15 mg/ml of the resulting catalyst contains 0.4 wt.% Pt + Rh ratio ~ 1 : 1.

Example 4.

100 grams of granulated-Al2O3brand EE-2 impregnated with 150 ml of an aqueous solution containing 2.0 mg/ml [Pd(NH3)4]Cl2. Then the granules are dried in air for 1.5 - 2 hours at a temperature of 100 - 150oC, then placed in a 150 ml aqueous solution containing 3.1 mg/ml (NH4)3[RhCl6]. The pellets are dried in air and calcined for one hour at a temperature of 550 - 620oC. the resulting catalyst contains 0.05 wt.% Pd + Rh ratio ~ 1 : 1.

Example 5.

The catalyst was prepared analogously to example 4.

However, the concentration of [Pd(NH3)4]Cl2was 40,0 mg/ml, and (NH4)3[RhCl6] to 6.2 mg/ml of the resulting catalyst contains 0.1 wt.% Pd + Rh ratio ~ 1 : 1.

Example 6.

The catalyst was prepared similarly to the method described in example 4. However, the concentration of [Pd(NH3)4] Cl2was 16.0 mg/ml, and (NH4)3[RhClabout allows to obtain a catalyst with a uniform and homogeneous distribution of the platinum metals in the surface layer (see table 1, 2), which leads to increased activity of the catalyst for conversion of NOx, CO, HC at a temperature of 150 - 160oC (see table 3, 4).

Testing of the catalysts was carried out as in laboratory conditions in a flow reactor with a programmed temperature change and chromatographic analysis of the gas and the engine stand firm SCHENK model WC-130, equipped with a control system DYNAMOT-CONTROL modes of load characteristics in the frequency range of rotation of the motor 1400 - 3400 min-1when the stoichiometric composition of the fuel mixture ( = 1). The sampling of exhaust gases was conducted on each mode twice: before and after the Converter. The gas analysis was performed using the Eclipse company HORIBA model MEXA-5120. Evaluation of the effectiveness of the catalyst was carried out on the engine with a displacement of 1800 cm3equipped with injection system BOSCH and system adaptation model VS-100 BOSCH.

Presented in tables 1 and 2 data on the content of platinum (palladium and rhodium in the surface layer of the catalyst indicate a uniform and homogeneous distribution of these elements in layers up to 4000 . Based on these results it can be concluded that the catalyst already in temperator, obtained by the proposed method? shows high activity even at a temperature of ~ 150oC. Thus, in tables 3 and 4 shows that in the temperature range 150 - 160oC can neutralize 40% NOxand 50% of CO and HC. Under these conditions, the catalyst obtained according to the method, not active. With increasing temperature (175 - 200oC) was observed 95% conversion of NOxand 100% conversion of CO and HC, i.e., in this temperature regime the proposed catalyst is two times more efficient than the known. This is important, because using it will allow you to neutralize the exhaust gases in a wider range of engine operation.

Thus, we can conclude that the proposed method for Pt/Rh and Pd/Rh catalysts provides a high efficiency of conversion of harmful emissions not only in the high temperature range (> 250oC), which is typical of known catalysts, but at a temperature of 150 - 160oC, i.e. at the time of engine start.

A method of obtaining a platinum-rhodium or palladium-rhodium catalyst on a ceramic carrier by successive impregnation of the carrier with aqueous solutions of platinum - or palladium compounds and registeruser the target of dichlorethylene platinum (II) Pt(NH3)4Cl2or palladium (II) Pd(NH3)4Cl2, dried, followed by treatment with a solution of ammonium salt of rhodium hexachloride (NH3)[RhCl6] with the formation on the surface of the carrier partially soluble binuclear complex

[M(NH3)4][Rh L6],

where M = Pt (II) or Pd (II);

L = Cl-and H2O.

 

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